In a valve on a processing plant in the chemical apparatus field, which has a valve housing, a feed flange and a discharge shaft, together with a valve seat arranged in the vicinity of the feed flange and an associated valve cone, at least the contacting parts of the valve seat and valve cone are made from metal. The inner wall of the valve seat formed as a surface of revolution is provided in the flow direction with two adjacent areas having different diameters and which are separated from one another by an edge. When the valve is closed, only the valve seat edge engages on the circumferential surface of the valve cone. In the first area facing the feed flange, the valve seat wall preferably has a substantially constant radius which continuously increases in the flow direction in the following second area, resulting in particularly reliable closing behavior. This can be further aided by an axially acting spring element. This construction is particularly advantageous for dosing a material flow from a pressure vessel connected to the feed flange which has a higher internal pressure than the valve housing.